One of the major stages for the production of a liquid crystal cell is the assembling of a first glass plate coated with a counter-electrode generally made of ITO (indium and tin oxide) with a second glass plate supporting etched patterns, these patterns constituting a matrix of display points or pixels. A glue joint disposed at the periphery of the first plate ensures the fixing of the two plates. Microballs provide a spacing of several microns between the two plates. This spacing is then filled with liquid crystals.
Generally speaking, an assembling machine is constituted as shown on FIGS. 1a-1d. These figures include (cf. FIG. 1a) an electrode carrier EC and a counter-electrode carrier CEC, both carriers being provided with prepositioning slugs. The first plate CE equipped with its counter-electrode and the glue joint UV and the second plate E equipped with its electrodes and spacers are positioned on the CEC and EC supports (FIG. 1b). Each of the two plates is kept in position via suction on its plate carrier. An arm B is provided so as to return the first plate CE and superimpose it on the second plate (FIG. 1c).
After alignment, the counter-electrode plate is laid on the electrode plate. Suction, which was keeping the first plate glued to the arm, is suppressed and the arm is brought back to an idle position (FIG. 1d).
After having cut suction under the electrode plate E, the cell may be disposed, the latter needing to then undergo polymerization of the glue by means of pressing under vacuum and being exposed to ultraviolet rays.
This type of machine does not enable one plate to be uniformly pressed onto the other plate and do not enable the glueing operation to take place in situ. In fact, if the two plates are properly placed opposite each other, they are not glued to each other at this stage. Therefore, it is necessary to have another working station, which implies an unloading of the preassembled cell followed by loading into a frame for under-vacuum pressing and isolation from the glue under ultraviolet rays. These multiple operations systematically result in having alignment defects.
Furthermore, these machines of the prior art do not make it possible to carry out a precise alignment of one plate onto the other plate at the time of preassembling. Now, in order to assemble a counter-electrode having an optical mask with an electrode having the shape of an active matrix, it is essential to know that the positioning precision is about several microns. Therefore, it is vital to have available means allowing for the precise alignment of marks located on the two plates.